Lytic and lysogenic cycles

- [Educator] What we're gonna do in this video is talk about two of the ways that a virus can leverage a cell to replicate the virus's DNA. So, the first is the lytic cycle, and this is what people often associate viruses doing. So, let's imagine a cell, and it's going to be a huge simplification right over here. Here's the cell and let's say that this is some DNA for that cell. Now, let's bring a virus into the picture. So, this virus is right over here. It attaches to the cell and it has some DNA that's, say, in that color. And so, what is going to happen is that DNA is going to make its way into the cell and then it's going to use the cell's machinery, namely the ribosomes. Let's just imagine that's a ribosome, that's a ribosome, that's a ribosome. And so, it hijacks some of that cell's machinery and it replicates that DNA and the proteins needed for that virus. And so then it just able to keep replicating, not just the DNA, or it could be RNA depending on the type of virus, but it actually can, in many ways, construct the entire virus itself. And it does it so much that eventually that cell can't function. So you have so much of this virus here that the cell is no longer functioning and then it blows up, it just, the cell dies, and all of that virus can now, so I'm just showing it. I almost imagine that the cell almost bursts, but one way you could think about it, the cell dies because it has all of that viral load inside of it. And then that virus goes out and moves on to potentially infect other cells. And this is kind of horror movie-like if you think about it. But this is the lytic cycle, right over here. Now, there's another cycle that in some ways is even creepier. And that is the lysogenic cycle. And these aren't necessarily separate. You can go from the lysogenic cycle into the lytic cycle. So in the lysogenic cycle. So let me draw the cell again and let me draw the cell's DNA, and lemme do that same orange color right over here. And let me draw that virus again. I'm making a little bit smaller 'cause I wanna do some interesting things here. So, in this case, that DNA can make its way in, but it doesn't immediately hijack the machinery of the cell to replicate the DNA and the proteins of the virus. But that DNA actually incorporates itself into the organism's DNA. It becomes part of the organism's genetic code, so to speak. And then when the organism itself replicates, or in this case, the cell replicates, so now it's just, there's just more cells that it is, it divides from one into two, from two into four, et cetera. Now, all of them have, all of them. Let me, so that was its original DNA. All of them have some of that viral DNA in it. And it turns out that even human DNA, the human genome has a lotta leftover virus DNA is what we believe from hundreds of millions, if not billions of years of this happening. And some of that is just sitting there dormant, or maybe it's even be put to use in some way. But there are situations where, potentially during stress or some other environmental conditions, that this in some ways wakes up. And you can go from this mode back into the lytic mode where all of a sudden this part gets activated and then you start producing many, many more viruses. And then the cell bursts the way that we talked about in the lytic cycle.